To better understand the observed differences in the mean 13C labeling of the TCA cycle intermediates between the two disease groups, the 13C labeling of individual TCA cycle intermediates were also evaluated in each individual MGUS and MM patient by assessing their fractional 13C enrichment (i.e., ratio of 13C enrichment of a TCA metabolite in CD138+ cells/CD138- cells such that a ratio of > 1 reflects higher 13C labeling of the specific metabolite in CD138+ cells). The gene discussed is SDC1; the disease is Miyoshi myopathy.